1. Field of the Invention
The present invention relates to a coordinate input device capable of detecting a position indicated by a pen or the like on an input surface and determining the coordinates of the position, and a control method therefor as well as a control program for implementing the method.
2. Description of the Related Art
In general, a coordinate input device is used to control a computer connected to the coordinate input device or write letters or figures by indicating a position on a coordinate input surface by a light-shading member, such as an indication tool or a finger, to thereby input the coordinates of the position.
Conventional coordinate input methods employed by the coordinate input devices of the above-mentioned type include ones using a resistance film, ones using ultrasound, ones using light, and other various methods. A method using light has been disclosed e.g. in U.S. Pat. No. 4,507,557.
In the coordinate input device proposed in U.S. Pat. No. 4,507,557, a retroreflective sheet is provided outside a coordinate input surface such that light projected from a light-projecting section can be reflected by the retroreflective sheet, and a light-receiving section receives the retroreflected light to detect a light amount distribution. The coordinate input device detects the angle of a spot shaded from light by an indication tool or a finger on the coordinate input surface, and determines the coordinates of a light-shaded position, i.e. an input position. Further, coordinate input devices have been disclosed in Japanese Laid-Open Patent Publications (Kokai) No. 2000-105671 and No. 2001-142642, in which a retroreflective member is provided around a coordinate input surface, such as a touch panel, and the coordinates of a portion shaded from retroreflected light from the retroreflective member are detected.
Generally, it is known that a coordinate input device is desirably provided with not only a pen-up/pen-down determining function, but also a proximity input function (proximity function), in view of accuracy in coordinate input operation. The pen-up/pen-down determining function enables discrimination between two basic states of an indication tool with respect to a coordinate input surface, i.e. a pen-up state (state before the indication tool or pen enters an input track) and a pen-down state (state after the indication tool or pen has entered an input track). The proximity input function enables detection of a coordinate position beforehand when the indication tool is in the pen-up state. Further, the proximity input function makes it possible to display the detected coordinates by a cursor in the pen-up state, and enables a user to carry out a coordinate input operation while confirming the detected coordinates displayed in advance by the cursor.
However, the coordinate input devices proposed, in U.S. Pat. No. 4,507,557 and Japanese Laid-Open Patent Publications (Kokai) No. 2000-105671 and No. 2001-142642 are not equipped with either the pen-up/pen-down determining function or the proximity input function, and therefore they have a problem in terms of accuracy in coordinate input operation. More specifically, in a coordinate input device operated using a touch panel, normally, a coordinate input operation is carried out on a coordinate input surface using an indication tool which is not provided with a state notifying means for notifying the pen-up/pen-down state, or using a finger. The coordinate input devices wherein the indication tool is not provided with the state notifying means are often configured such that when the position of the indication tool is detected, it is determined that the indication tool is in the pen-down state. Of course, such coordinate input devices are not provided with the proximity input function.
On the other hand, coordinate input devices provided with the pen-up/pen-down determining function in view of accuracy in coordinate input operation have been disclosed e.g. in Japanese Laid-Open Patent Publications (Kokai) No. 2002-091701 and No. 2001-084106. In the coordinate input device proposed in Japanese Laid-Open Patent Publication (Kokai) No. 2002-091701, a light-shading-type touch panel is used, and the pen-up/pen-down state is determined based on the degree of light shading in coordinate input operation. In the coordinate input device proposed in Japanese Laid-Open Patent Publication (Kokai) No. 2001-084106, the pen-up/pen-down state of an indication tool is determined based on a change in distance between the indication tool and the coordinate input surface as well as a change in the level of depth of a dip in light intensity distribution (a valley between a falling edge and a following rising edge of a light intensity distribution waveform).
However, the coordinate input devices disclosed in Japanese Laid-Open Patent Publications (Kokai) No. 2002-091701 and No. 2001-084106 suffer from the following problems.
First, a description will be given of problems with the coordinate input device proposed in Japanese Laid-Open Patent Publication (Kokai) No. 2002-091701. In the light-shading-type touch panel of the above-mentioned type, an area (retroreflective zone) where reflected light for detecting light shading passes forms a relatively thin layer in parallel with the coordinate input surface. However, the distance between this thin layer and the coordinate input surface is not necessarily accurately constant over the entire area. Therefore, it is difficult to determine the pen-up/pen-down state accurately by the above described method. Further, since the retroreflective zone is thin, a range enabling detection of light shading is narrow, which makes it difficult to fully exert the proximity input function.
Next, a description will be given of problems with the coordinate input device proposed in Japanese Laid-Open Patent Publication (Kokai) No. 2001-084106, with reference to FIGS. 28, 29, and 7A to 7C.
In this coordinate input device, when a change in distance between the indication tool and the coordinate input surface, or more precisely, the rate of change in distance therebetween becomes smaller than a predetermined rate, it is determined that a pen-down event has occurred.
Some pens used for coordinate input devices of this type do not have a constant shape. In other words, they can be deformed into some shape. Many of them are configured to be deformed upon abutment of a tip thereof against a coordinate input surface so as to improve a drawing touch or simply to imitate the touch of a conventional pen.
As shown in FIG. 28, this type of pen is in a shape indicated by a symbol A, for example, when it is not in contact with a coordinate input surface f (by a distance of h), and turns into a shape indicated by a symbol B, C, or D when it is brought into contact with the coordinate input surface f and then further pressed against the coordinate input surface f. It should be noted that A′ indicates a case without deformation.
A pen which can be deformed into the shape B has a tip formed e.g. of a soft rubber-like material. A pen which can be deformed into the shape C has a tip to which is attached a part slidable like a switch. Further, a pen which can be deformed into the shape D has a brush-like tip deformable into a tail-like portion.
In general, in the coordinate input device of a light-shading type proposed in Japanese Laid-Open Patent Publication (Kokai) No. 2001-084106, a retroreflective zone is so thin that a range within which light shading can be detected is not more than several millimeters in thickness in the direction perpendicular to the coordinate input surface. For this reason, an adequate proximity input function cannot be provided. As a solution to this problem, the use of a pen which can be deformed into the shape indicated by the symbol B, C, or D can be envisaged so as to realize a virtually adequate proximity input function (see h0 and |h0| in FIG. 28).
However, even when the pen which can be deformed as described above is used, the coordinate input device proposed in Japanese Laid-Open Patent Publication (Kokai) No. 2001-084106 determines the occurrence of a pen-down event based on a change in the distance between the indication tool and the coordinate input surface. For this reason, when the distance between the indication tool and the coordinate input surface becomes equal to 0 (i.e. a stage indicated by the symbol A′), it is determined that the indication tool is in the pen-down state, and therefore the occurrence of a pen-down event cannot be judged from abutment of the indication tool against the coordinate input surface, including predetermined mechanical deformation (|h0|) as shown by the case B, C, or D. In short, even when the deformable pen is used, the virtually adequate proximity input function cannot be realized.
Further, in Japanese Laid-Open Patent Publication (Kokai) No. 2001-084106, the pen-up/pen-down state of the indication tool is determined based on a change in the level of depth of a dip in light intensity distribution.
In the following, this point will be studied.
Assuming that a pen 105 having a predetermined shape is approaching a coordinate input surface, insofar as the tip of the pen 105 is within a retroreflective zone 100 as shown in a state indicated by P1 in FIG. 29, the depth (Dpth) and width (Wd) of the valley of the light shading-dependent waveform increases as the pen tip becomes closer to the coordinate input surface 104 (see FIG. 7A).
Further, when the tip end of the pen 105 reaches the lower edge of the retroreflective zone 100 (i.e. a position indicated by P2 in FIG. 29), the depth Dpth of the valley reaches a maximum Dpth value Dpth_max (see FIG. 7B), and from then on (i.e. in positions indicated by P2 and P3 (P4) in FIG. 29), the Dpth value never changes but only the width (Wd) of the valley of the light shading-dependent waveform increases (see FIG. 7C).
This is because when the tip of the pen 105 reaches a position not higher than the lower edge of the retroreflective range 100 (i.e. below the position indicated by P2 in FIG. 29), light is substantially 100% blocked by the approximately central portion of the pen 105, and therefore there is no more light shading by the central portion of the pen 105.
As described above, insofar as the change in the level of depth of the dip in the light intensity distribution is concerned, when the pen 105 reaches the position indicated by P2 in FIG. 29, the depth of the dip reaches its maximum value, and even when the pen 105 further moves to the positions indicated by P2 and P3 (P4) in FIG. 29, the depth of the dip is held constant.
However, in the case where determination of the pen-up/pen-down state of the indication tool is performed based a change in the level of depth of a dip in light intensity distribution as in Japanese Laid-Open Patent Publication (Kokai) No. 2001-084106, the range from the position P2 to the position P3 (P4) is a dead zone for the function of detecting a pen. For this reason, the pen-down state is determined only in a stage where the pen 105 is in the vicinity of the position 2 or before the stage, but cannot be determined e.g. when the pen 105 is in the vicinity of the position P3 or P4.
In general, it is desirable, in view of operability of the pen 105, that determination of the pen-down state should be performed when the pen is at a position closest possible to the position for abutment against the coordinate input surface. However, the coordinate input device proposed in Japanese Laid-Open Patent Publication (Kokai) No. 2001-084106 is not capable of determining the pen-down state in the vicinity of the position P3 or P4 of the pen 105, which is a negative aspect of the coordinate input device in terms of the operability of the pen 105.
To solve the above-described problems with the coordinate input devices disclosed in Japanese Laid-Open Patent Publications (Kokai) No. 2002-091701 and No. 2001-084106, a method has been proposed which uses a special pen equipped with a function of transmitting a pen-down signal to the light-shading-type touch panel. More specifically, in this method, a switch is provided e.g. on the tip of the pen, and when the pen abuts against the coordinate input surface, the switch is depressed, whereby the pen-down signal is transmitted in real time by infrared rays, ultrasound, electromagnetic waves, or the like. This method makes it possible to perform an appropriate determination of the pen-up/pen-down state.
However, the light-shading-type touch panel provided with the indication tool having the above-mentioned communication function has the following disadvantages: First, it is necessary to transmit the pen-down signal, and hence the pen per se is complicated (expensive, larger in size). Secondly, since it is necessary to transmit the pen-down signal, a power supply (battery or the like) is needed for the signal transmission. Thirdly, since it is necessary to transmit the pen-down signal, the thickness of the retroreflective zone 100 is limited to prevent an excessive increase in depth of a frame portion surrounding the coordinate input surface, and therefore the range within which light shading can be detected is narrowed, which makes it difficult to fully exert the proximity input function.